JP2006107830A - Film formation device and film formation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To equalize the thickness of a catalyst layer of an electrode for a fuel cell. <P>SOLUTION: After slurry of an aggregated flock containing catalyst particles is fabricated by a slurry fabrication part 20, compressed air is introduced into the slurry by a pressurized water processing part 30 to dissolve the air to form pressurized water slurry. When it is transferred to a slurry sprayer 35, oversaturated air incapable of being dissolved by the atmospheric pressure is attached to the aggregated flock as air bubbles, and buoyancy by the air bubbles acts on the aggregated flock to delay its sinking speed. Thereby, the aggregated flock is prevented from being precipitated immediately after supplying the slurry on carbon paper 50, whereby the thickness of a catalyst layer formed on the carbon paper 50 is equalized. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a film forming apparatus and a film forming method, and more particularly, is used for forming a catalyst layer of an electrode for a fuel cell, and forms a film such as catalyst particles on a filter medium such as carbon paper by filtering slurry containing catalyst particles. The present invention relates to a film forming apparatus and a film forming method.

  In general, a fuel cell includes an electrode in which an electrolyte layer is sandwiched between a fuel electrode and an air electrode, and a base material provided with a gas diffusion layer and a gas flow path is attached to the electrode. Gas diffusion layers and base materials with gas flow paths are required to have electrical conductivity and corrosion resistance in addition to gas diffusibility. Usually, porous carbon paper is used for gas diffusion layers, and base materials with gas flow paths are also used. Each uses porous carbon.

  In order to adjust the reaction heat to a certain temperature, unit cells using such a material are stacked with 5 to 8 carbon separators in between to prevent direct contact between hydrogen and air. Attach one cooling plate. Then, a battery stack is formed by repeatedly laminating several unit cells separated by a separator and one unit of cooling plate so that the number of cells required for the amount of generated power is obtained.

  The fuel electrode and the air electrode of the fuel cell can be formed as follows, for example. First, a slurry containing catalyst particles such as platinum and a fluororesin such as polytetrafluoroethylene (PTFE) is formed. This is suction filtered using carbon paper as a filter, and catalyst particles and the like contained in the slurry are deposited on the carbon paper. Then, after removing the solvent and moisture by drying, in order to give the catalyst layer appropriate water repellency and increase the binding property between the catalyst layer and the carbon paper, the melting temperature of the fluororesin is about approx. Thermocompression bonding with a press or the like is performed at a temperature of about 330 ° C. Thereby, a fuel electrode or an air electrode in which the catalyst layer and the gas diffusion layer are integrated is formed.

  As described above, several methods using filtration for forming a catalyst layer have been proposed. For example, an anionic surfactant is used to improve the dispersion state of catalyst particles and PTFE in a slurry, and suction filtration is performed. In some cases, a good catalyst layer is formed on carbon paper (see Patent Document 1). Further, after the slurry is suction filtered to form a catalyst layer, the second slurry containing SiC particles is suction filtered to form an SiC layer on the catalyst layer, and the SiC layer is removed through heat drying and firing. Thus, there is also one that suppresses the occurrence of cracks during heating and drying of the catalyst layer and peeling during hot pressing (see Patent Document 2).

In addition, the raw material mixture containing catalyst particles and electrolyte is prepared at different mixing ratios, and the slurry mixed with them is pressure filtered to utilize the difference in specific gravity, so that the electrolyte is more on the surface side, the carbon paper side There has also been proposed a method of forming a catalyst layer that decreases with time (see Patent Document 3).
JP 2001-57216 A JP 2002-373664 A JP-A-9-180730

  However, when the catalyst layer is formed by filtration of the slurry containing the catalyst particles as described above, the catalyst particles etc. start to settle, although there is a difference when the slurry is supplied onto the carbon paper. If the catalyst particles and the like are quickly precipitated after the slurry is supplied, a catalyst layer having a non-uniform thickness is easily formed on the carbon paper after filtration.

FIG. 5 is an example of a catalyst layer formed on the carbon paper after filtration.
When the catalyst particles in the slurry start to settle after being supplied onto the carbon paper 100, for example, a catalyst having a non-uniform thickness on the carbon paper 100 after filtration, such as being thick at the center and thin at the periphery. The layer 101 may be formed. If the thickness of the catalyst layer 101 is not uniform, a gap may be formed between the catalyst layer 101 and the gas flow may be non-uniform, leading to a decrease in power generation capacity and variations.

  Conventionally, in order to avoid such a problem, non-uniformity in the thickness of the catalyst layer has been made by performing filtration in several times or allowing the filtrate to flow smoothly on the filtration device side. However, as the size of the fuel cell increases, it is not rare to form an electrode of 1m size, and the suction / pressure balance and in-plane variation of the slurry supply amount on the carbon paper are increased by increasing the filtration area. Is likely to occur.

  In addition, it is conceivable to avoid unevenness of the thickness of the formed catalyst layer by stirring the slurry supplied on the carbon paper before or during filtration. If the catalyst particles and the like are precipitated quickly, the effect cannot be expected by simply stirring.

  The present invention has been made in view of these points, and can be formed with a uniform thickness when the slurry is filtered to form a film of particles in the slurry on the filter medium. An object is to provide a film apparatus and a film forming method.

  In the present invention, in order to solve the above problem, in a film forming apparatus for filtering a slurry to form a film on a filter medium, air is dissolved in the slurry before filtration under pressure, and the slurry in which the air is dissolved is decompressed. And forming a film of the particles on the filter medium by filtering the slurry in which bubbles are attached to the particles included in the slurry, and filtering the slurry in which the bubbles are attached to the particles. Provided.

  When air is dissolved in the slurry under pressure before filtration and the pressure is reduced, air bubbles adhere to the particles in the slurry. This is because when the slurry in which air is dissolved under pressure is depressurized, supersaturated air adheres to the granules as bubbles in the depressurized environment. Thus, since the buoyancy by a bubble works in the liquid to the particle | grains to which the bubble adhered, it becomes possible to delay the sedimentation speed. Therefore, when the slurry is filtered to form a film on the filter medium, even if the slurry is supplied onto the filter medium, for example, by using convection generated in the slurry at the time of supply or forcibly stirring, the granules immediately after the supply It is possible to suppress the occurrence of non-uniform precipitation.

  Further, in the present invention, in the film forming method for filtering the slurry and forming a film on the filter medium, air is dissolved in the slurry before filtration under pressure, and the slurry in which the air is dissolved is decompressed to form the slurry. There is provided a film forming method characterized in that bubbles are attached to the contained particles and the slurry in which the bubbles are attached to the particles is filtered to form the film of the particles on the filter medium.

  According to such a film forming method, it is possible to suppress the sedimentation rate of the particles in the slurry by using bubbles, and to suppress non-uniform sedimentation on the filter medium.

  In the present invention, air is dissolved in the slurry before filtration under pressure, and the pressure is reduced to allow bubbles to adhere to the particles in the slurry, thereby slowing the sedimentation rate. This makes it possible to suppress non-uniform precipitation of particles that may occur immediately after the slurry is supplied onto the filter medium, so that a film of particles can be formed on the filter medium with a uniform thickness. .

  When such a film forming apparatus and film forming method are used for forming a catalyst layer of a fuel cell electrode, a slurry containing catalyst particles and the like is filtered to form a porous carbon material such as carbon paper with a uniform thickness. A catalyst layer can be formed. As a result, a high-performance and highly reliable fuel cell can be realized.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings, taking as an example a case where the present invention is applied to formation of a catalyst layer of a fuel cell electrode.
FIG. 1 is a schematic view of a film forming apparatus.

The film forming apparatus 10 shown in FIG. 1 includes a slurry preparation unit 20, a pressurized water treatment unit 30, and a slurry filtration unit 40.
The slurry preparation unit 20 includes a catalyst dispersion tank 21, a PTFE dispersion tank 22, and a flocculation tank 23. Each of these tanks includes a catalyst slurry tank 24, a PTFE solution tank 25, and a flocculant tank 26, respectively. , 27b, 27c. In addition, stirring and dispersing machines 28a, 28b, and 28c are attached to the catalyst dispersion tank 21, the PTFE dispersion tank 22, and the aggregation tank 23, respectively.

  From the catalyst slurry tank 24, a slurry of a mixture of catalyst particles such as platinum black and a carbon-supported platinum catalyst, pure water, and if necessary an anionic surfactant is added to the catalyst dispersion tank 21 through a pipe 27a. Thus, the slurry charged into the catalyst dispersion tank 21 is stirred by the stirring and dispersing machine 28a so that the contained particles are kept in a constant dispersion state.

  The catalyst dispersion tank 21 and the PTFE dispersion tank 22 are connected by a pipe 27d, and the slurry in the catalyst dispersion tank 21 is transferred to the PTFE dispersion tank 22 by a pump 29a provided in the middle of the pipe 27d. It has become. A predetermined amount of PTFE dispersion is supplied from the PTFE solution tank 25 through the pipe 27 b to the PTFE dispersion tank 22, and in the PTFE dispersion tank 22, the supplied PTFE dispersion and catalyst dispersion tank 21 are provided. The slurry from the above is stirred by the stirring and dispersing machine 28b.

  The PTFE dispersion tank 22 and the coagulation tank 23 are connected by a pipe 27e, and the slurry in the PTFE dispersion tank 22 is transferred to the coagulation tank 23 by a pump 29b provided in the middle of the pipe 27e. ing. A predetermined amount of an aggregating agent, for example, an acid such as phosphoric acid or a polymer aggregating agent is introduced into the aggregating tank 23 through the pipe 27c. The flocculant and the slurry from the PTFE dispersion tank 22 are stirred by the stirring and dispersing machine 28c.

  The pressurized water treatment unit 30 has a pressurized water tank 31, and the slurry containing the aggregated floc generated in the aggregation tank 23 is transferred to the pressurized water tank 31 by a pipe 27 f and a pump 29 c provided in the middle thereof. It has come to be.

  An air compressor 32 is connected to the pressurized water tank 31 and a pressure release valve 33 for controlling the internal pressure is provided. Pressurized water under a certain pressure is applied to the slurry in the pressurized water tank 31 by compressed air from the air compressor 32. Processing is performed. The slurry after the pressurized water treatment (referred to as “pressurized water slurry”) is sent to the slurry spreader 35 from the pressurized water slurry transfer port 34 provided at the bottom of the pressurized water tank 31.

  The slurry filtration unit 40 includes a suction filtration device 41 and a frame 42, and a carbon paper 50 that is a porous body (filter material) on which a catalyst layer is to be formed is set between the suction filtration device 41 and the frame 42. The The pressurized water slurry is sprayed inside the frame 42 by the slurry sprayer 35. Further, the slurry filtering unit 40 is provided with a stirring plate 44 for stirring the slurry 43 dispersed and accumulated in the frame 42, and the stirring plate 44 can reciprocate in the frame 42. It is configured as follows.

Next, a method for forming a catalyst layer using the film forming apparatus 10 having the above configuration will be described.
FIG. 2 is an example of the catalyst layer formation flow.
For example, when an anionic surfactant is used, it is first added to pure water and stirred to prepare a dispersion medium containing the surfactant. Then, the dispersion medium and catalyst particles such as a carbon-supported platinum catalyst are charged into the catalyst slurry tank 24, which is put into the catalyst dispersion tank 21 and stirred by the stirring and dispersing machine 28a. Thereby, a slurry in which the catalyst particles are dispersed in the dispersion medium is formed.

  Then, after this slurry is transferred to the PTFE dispersion tank 22 using the pump 29a, the PTFE dispersion liquid charged in the PTFE solution tank 25 is also charged into the PTFE dispersion tank 22, and these are stirred by the stirring and dispersing machine 28b. Stir. This forms a slurry in which the catalyst particles and PTFE are dispersed in the dispersion medium.

  Then, after the slurry is transferred to the agglomeration tank 23 using the pump 29b, the aggregating agent charged in the aggregating agent tank 26 is charged into the aggregating tank 23, and these are agitated by the agitating and dispersing machine 28c. By adding the flocculant, the surfactant loses its effectiveness, and a slurry is formed containing flocs (aggregated flocs) that are agglomerated without separating the catalyst particles and PTFE. By making the catalyst particles or the like into such a form of agglomerated floc, clogging of the filter medium is suppressed and suction filtration is facilitated. This slurry is transferred to the pressurized water tank 31 using the pump 29c, and a pressurized water process is performed.

  After the slurry is transferred to the pressurized water tank 31, compressed air is introduced from the air compressor 32 into the pressurized water tank 31 to dissolve the air in the slurry under pressure, and undissolved air is extracted from the pressure release valve 33 to form a pressurized water slurry. To do. The inside of the pressurized water tank 31 is controlled to 0.5 MPa, for example.

  Thereafter, the pressurized water slurry is sent from the pressurized water slurry transfer port 34 to the slurry spreader 35. At that time, by depressurizing to atmospheric pressure, supersaturated air that cannot be dissolved under atmospheric pressure becomes fine bubbles in the aggregated floc. It comes to adhere.

Here, FIG. 3 is a schematic view of an agglomerated floc to which bubbles are attached.
As shown in FIG. 3, the aggregated floc 60 contained in the pressurized water slurry has a large number of bubbles 61 attached to its surface and the like when returned to atmospheric pressure. Thereby, the buoyancy by the bubble 61 comes to act on the aggregation floc 60 in the liquid.

  Such slurry is spread on the carbon paper 50 in the frame 42 from the slurry spreader 35 and sucked by the suction filtration device 41 from the opposite side. At that time, since the buoyancy of bubbles acts on the aggregated flocs in the slurry, the sedimentation speed thereof becomes slower than the case where the pressurized water treatment is not performed. Here, the slurry in the frame 42 is subjected to suction filtration while being stirred using the stirring plate 44 to form a catalyst layer.

FIG. 4 is a schematic view of the catalyst layer after suction filtration.
Due to the pressurized water treatment effect and the agitation effect, the catalyst layer 51 is formed on the carbon paper 50 with good uniformity as shown in FIG.

  After suction filtration, pure water is poured into the frame 42 to wash the flocculant remaining in the catalyst layer, and drying and firing are performed. Thereby, the surfactant is removed from the catalyst layer, and PTFE is melted to have water repellency.

  As described above, when the catalyst layer is formed on the carbon paper by suction filtration, the aggregation flocs in the slurry to be suction filtered are treated with pressurized water to reduce the sedimentation speed. As a result, the sedimentation of the aggregated floc from the time when it is spread on the carbon paper is delayed. In addition, the slurry to be suction filtered can be mixed with a pressurized water treatment effect and a stirring effect to suppress non-uniform sedimentation of agglomerated flocs and form a catalyst layer with a uniform thickness on carbon paper. become able to.

  In the above description, when the catalyst particles are mixed with a dispersion medium obtained by adding an anionic surfactant to pure water to form a slurry, a dispersion medium containing an anionic surfactant is charged into the catalyst dispersion tank 21. Alternatively, only the catalyst particles may be dropped from the catalyst slurry tank 24, and these may be dispersed by stirring in the catalyst dispersion tank 21 with the stirring and dispersing machine 28a.

  In the above description, in the catalyst dispersion tank 21, the PTFE dispersion tank 22, and the agglomeration tank 23, the slurry in each tank is stirred and dispersed by the stirring and dispersing machines 28a, 28b, and 28c. , 28b, 28c, or together with the stir dispersers 28a, 28b, 28c, an ultrasonic dispersing device such as a homogenizer may be used to disperse the slurry.

  Although the case where the catalyst layer is formed by suction filtration has been described as an example here, the catalyst layer may be formed by pressure filtration.

  INDUSTRIAL APPLICABILITY The present invention is widely applicable not only to the formation of a catalyst layer for a fuel cell electrode but also to the use of forming a film by filtering the slurry and depositing the granular material in the slurry on the filter medium.

It is the schematic of a film-forming apparatus. It is an example of a catalyst layer formation flow. It is a schematic diagram of the aggregation floc to which the bubble adhered. It is a schematic diagram of the catalyst layer after suction filtration. It is an example of the catalyst layer formed on the carbon paper after filtration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Film-forming apparatus 20 Slurry preparation part 21 Catalyst dispersion tank 22 PTFE dispersion tank 23 Coagulation tank 24 Catalyst slurry tank 25 PTFE solution tank 26 Coagulant tank 27a, 27b, 27c, 27d, 27e, 27f Piping 28a, 28b, 28c Stirring dispersion Machine 29a, 29b, 29c Pump 30 Pressurized water treatment unit 31 Pressurized water tank 32 Air compressor 33 Pressure release valve 34 Pressurized water slurry transfer port 35 Slurry spreader 40 Slurry filtration unit 41 Suction filtration device 42 Frame 43 Slurry 44 Stirring plate 50 Carbon paper 51 Catalyst Layer 60 Agglomerated floc 61 Air bubbles

Claims (6)

In a film forming apparatus that forms a film on a filter medium by filtering slurry,
The slurry in which air is dissolved in the slurry before filtration under pressure, the slurry in which the air has been dissolved is depressurized, bubbles are attached to the particles included in the slurry, and the bubbles are attached to the particles. A film forming apparatus, wherein the film of the particles is formed on the filter medium by filtration.   The film forming apparatus according to claim 1, further comprising means for stirring the slurry supplied to the filter medium with bubbles attached to the granules.   The film forming apparatus according to claim 1, wherein the filter medium is a porous carbon material, and the slurry includes catalyst particles constituting a catalyst layer used for an electrode of a fuel cell. In a film forming method for forming a film on a filter medium by filtering slurry,
The slurry in which air is dissolved in the slurry before filtration under pressure, the slurry in which the air has been dissolved is depressurized, bubbles are attached to the particles included in the slurry, and the bubbles are attached to the particles. A film forming method comprising: filtering to form a film of the particles on the filter medium.   5. The film forming method according to claim 4, wherein, when the slurry in which bubbles are attached to the granules is filtered, the slurry is stirred after the slurry is supplied onto the filter medium. The film forming method according to claim 4, wherein the filter medium is a porous carbon material, and the slurry contains catalyst particles constituting a catalyst layer used for an electrode of a fuel cell.

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